The discovery of more than 3,450 exoplanets in the past 25 years has raised the possibility that life might have arisen on some world besides Earth. However, much remains a mystery about how life might have originated on this planet, much less a distant world.
To shed light on the evolution of life, lab experiments have sought to simulate what the primordial seas of the early barren Earth might have been like. “We are trying to reveal how this planet was before life appeared,” said crystallographer Juan Manuel García-Ruiz of the Spanish National Research Council and the University of Granada in Spain.
Prior research found that in the absence of the organic chemicals that make up life, minerals could organize themselves into complex formations resembling biological structures and even primitive organisms. Those studies looked at inorganic mineral growth within alkaline liquids rich in silica — the chemical that makes up sand and glass — and found that the minerals assembled themselves into formations resembling “the sensual shapes of life,” García-Ruiz said. These include “silica gardens” made of chimney-like tubes and filmy structures that possess catalytic properties, as well as “biomorphs” with coral-like and flower-like patterns, some of which even mimic the shape of ancient fossilized microbes.
These complex mineral structures can serve as catalysts for chemical reactions that produce important organic molecules, such as the amino acids that make up proteins and the bases that make up DNA. From ideal cauldrons such as these, life may have originated here on Earth and even beyond.
Silica-carbonate biomorphs grown with natural Ney spring water. Credit: García-Ruiz et al. Sci. Adv. 2017;3:e1602285
While studies prior to this one used liquids created in the lab as a medium, García-Ruiz and his colleagues grew minerals in samples taken from the Ney spring in California, located in an abandoned spa called Aqua de Ney at Ney Creek, a tributary of the Sacramento River. The team wanted to know if naturally occurring versions of these fluids might produce the same formations and found that complex mineral structures were able to form in the spring water.
“Our results demonstrate that these fascinating structures can be self-assembled with natural water from springs,” García-Ruiz said. “It means that these phenomena are geochemically possible.”
Self-assembled calcite mesocrystals grown with Nay springs waters. Credit: García-Ruiz et al. Sci. Adv. 2017;3:e1602285
This unusual spring water was naturally about as alkaline as household ammonia. While such water is now very rare on Earth, it “was very much frequent during the early years of this planet, before life appeared on it,” García-Ruiz said. Despite the strong alkalinity, the researchers did not have to take any special precautions while collecting it “apart from avoiding contact for long periods of time,” García-Ruiz said. “Believe or not, the water of this well was used in the 19th century and early years of the 20th century for skin treatment. I would not recommend it. But the atmosphere of the site is very charming.”
The silica gardens formed when pellets of metal salts were placed in vials of the spring water. These silica gardens developed hollow tubes that burst with carbon dioxide bubbles, potentially enhancing the amount of surface area available to catalyze reactions. Biomorphs also formed in the spring water when carbon dioxide gas was bubbled through the Petri dishes, and even when the Petri dishes were tightly sealed and left alone. The biomorphs had smooth, curved surfaces, as well as twisted ribbon shapes reminiscent of microbes and crystal structures similar to those seen in sea urchins and mollusk shells.
An inorganic tube precipitates out of a high-pH silica water from Ney spring. (scale bar is 20µm). Credit: Juan Manuel García-Ruiz
An intriguing aspect of this work is that this spring water resulted from a geological process known as serpentinization, which also can produce organic compounds in the absence of life. “Our demonstration that raw organic compounds for prebiotic chemistry and mineral self-assembly may have shared the same scenario in the earliest Earth and Earth-like planets opens a fascinating possibility of coupling both phenomena,” García-Ruiz said.
Future research can analyze other alkaline silica-enriched water, such as those seen in the Rift Valley in Africa, García-Ruiz said. He and his colleagues Elias Nakouzi, Electra Kotopoulou, Leonardo Tamborrino and Oliver Steinbock detailed their findings online March 17 in the journal Science Advances.